The present invention relates to an automatic document feeder for feeding a sheet or a manuscript onto a platen of a copy machine or an image reader, or for feeding a sheet to the copy machine.
In conventional automatic document feeders, one of the document feeders is provided with a sheet mounting portion, a roller rotationally contacting and transferring a sheet mounted on the sheet mounting portion, and a pressure device for urging the sheet located on the sheet mounting portion onto the roller. When sheets or manuscripts are supplied onto the sheet mounting portion, the sheets are fed into a space between the roller and the pressure device from an upstream side of the sheet transfer direction.
In case the roller is a semi-circular roller having a semi-circular portion and a non-circular or cutout portion in cross section, when a switch is actuated, an initial operation is made. In the initial operation, the semi-circular roller rotates such that the semi-circular portion is located under a guide plate at the sheet mounting portion and the cutout portion is located under the guide plate. As a result, the semi-circular roller is positioned in an initial condition where the semi-circular roller does not contact the sheet to be fed.
In the former case, when the sheets are mounted, the front edges of the sheets may abut against the roller projecting from the sheet mounting portion. Thus, the sheets may not properly set on the sheet mounting portion. Sometimes, the sheets are damaged.
In the later case, before the switch is initially turned on, the semi-circular roller may not be in the initial condition. Thus, when the sheets are mounted, the sheets may be damaged or may not be properly set, as in the former case.
Accordingly, one object of the invention is to provide a sheet feeding mechanism for an automatic document feeder, wherein when the sheets are supplied to a portion between the roller and the pressure device from an upstream side of the roller, the sheets do not abut against or hit the roller and the sheets can be smoothly set on the sheet mounting portion.
Another object of the invention is to provide a sheet feeding mechanism as stated above, wherein the sheets can be set reliably onto the sheet mounting portion without causing damage to the sheets.
A further object of the invention is to provide a sheet feeding mechanism as stated above, wherein a rotational power for an operation mechanism, e.g. the semi-circular roller, can be reduced.
Further objects and advantages of the invention will be apparent from the following description of the invention.